diff --git a/nova/tests/unit/virt/libvirt/test_driver.py b/nova/tests/unit/virt/libvirt/test_driver.py
index 2e6923de8b..1d89291647 100644
--- a/nova/tests/unit/virt/libvirt/test_driver.py
+++ b/nova/tests/unit/virt/libvirt/test_driver.py
@@ -16275,6 +16275,7 @@ class LibvirtDriverTestCase(test.NoDBTestCase):
                      mock_build_device_metadata, mock_set_host_enabled,
                      mock_write_to_file,
                      exists=None):
+        self.flags(instances_path=self.useFixture(fixtures.TempDir()).path)
         mock_build_device_metadata.return_value = None
         mock_supports_direct_io.return_value = True
 
diff --git a/nova/tests/unit/virt/libvirt/test_imagebackend.py b/nova/tests/unit/virt/libvirt/test_imagebackend.py
index 5d548f8746..b51811be97 100644
--- a/nova/tests/unit/virt/libvirt/test_imagebackend.py
+++ b/nova/tests/unit/virt/libvirt/test_imagebackend.py
@@ -1684,6 +1684,7 @@ class BackendTestCase(test.NoDBTestCase):
     def setUp(self):
         super(BackendTestCase, self).setUp()
         self.flags(enabled=False, group='ephemeral_storage_encryption')
+        self.flags(instances_path=self.useFixture(fixtures.TempDir()).path)
         self.INSTANCE['ephemeral_key_uuid'] = None
 
     def get_image(self, use_cow, image_type):